During the production of oil and gas from subterranean formations located thousands of feet below the sea floor, water is commingled with the oil and gas and brought to the surface facilities for treatment. The oil and gas must be separated from the aqueous phase prior to being transported to the inland refineries. This aqueous phase referred to as produced water must also be treated to remove all insoluble oil and grease such that when extracted with solvents comply with local regulations for discharge into the environment. These produced waters can range from 1% to 99% of total fluid during oil and gas production.
Produced water contains water-insoluble and marginally water-soluble petroleum oil components, generally in amounts of about 30 to about 2,000 parts per million, that are the subject of EPA regulations because of their toxicity and sheen causing potential on the surface of the ocean. The water insoluble and marginally water-soluble petroleum oil components may not be returned to the ocean in a concentration greater than 29 parts per million from an off-shore petroleum oil production facility because these materials have a tendency to separate from ocean water, due to the relatively low ocean water temperature, and agglomerate in the form of suspended droplets that result in a sheen on the surface of the ocean. Higher concentrations of organics also cause toxicity concerns for the indigenous species in the sea.
Offshore drilling and production platforms used for recovering oil from subterranean formations disposed beneath ocean water includes a number of structural support legs for supporting a plurality of work deck areas at substantial heights above the water level, e.g., disposed from 40 to 100 or more feet above sea level. During the recovery of oil at one or more of these work deck areas, oil, grease and other hydrocarbons are unavoidably spilled onto the deck area(s) and it is not permissible to discard these hydrocarbons into the ocean water. Such work deck areas or platform surfaces are constructed to be fluid-impermeable in order to contain the spilled hydrocarbons on the work deck areas. These hydrocarbons, such as recovered oil, grease, surfactants and other organic contaminants, are directed from the work deck or platform areas, either by water washing or rainwater, into a sump pump container or sump tank where the water and oil separate by gravity so that the water can be removed from a lower portion of the sump tank, for conveyance back to the ocean, and the oil can be pumped from an upper portion of the sump tank into an oil recovery container so that the oil is not returned to the ocean.
These contained deck areas on offshore structures collect a significant amount of water during periods of high rainfall. The rainwater and entrained hydrocarbons, particularly recovered oil, grease and surfactants, are conveyed to the sump tank or collection tank through a gravity drain system from each of the work deck areas. These sump tanks rely on retention time as the primary oil/water separation mechanism in order to skim the lighter density hydrocarbons from a top of the sump tank so that the water can be returned to the ocean.
The sump tanks presently used on offshore platforms suffer from a number of major drawbacks which result in significant amounts of hydrocarbons, particularly oil, paraffins, grease, and refined hydrocarbons being returned to the ocean causing significant ecological contamination. One major drawback of the presently used sump tanks is that they are designed for a maximum of about three inches of rainwater per hour. It has been found that it is not uncommon to experience eight to ten inches of rainfall per hour in areas such as the Gulf of Mexico. Another major drawback of the sump tanks presently used on offshore drilling platforms is that a tank containing a layer of oil disposed above a layer of water will lose the water by evaporation over an extended dry period and the oil layer, as a result, will coat the inside surfaces of the sump tank. This phenomena is known in the art as sheening. As a result of the sump tank sheening, water generated from even a modest rain shower, after this drying period, carries the oil through a water leg or drain portion of the sump tank as the water initially washes lower inner surfaces of the sump tank, thereby carrying the oil to the ocean.
Another water treatment problem associated with offshore oil and gas producing platforms is the treatment of the aqueous solutions used in acid fracturing processes. Specifically, acidic solutions are commonly pumped down under pressure to cause fractures in the oil producing regions of the formation. As these acidic solutions are returned to the surface, they are often contaminated with oil or hydrocarbons. As discussed above with respect to produced water and rainwater, the hydrocarbons must be removed from the solutions before the water is returned to the ocean.
Another problem associated with all auxiliary equipment used on oil platforms is the need for equipment to be designed in a space efficient manner. Specifically, auxiliary equipment, including water treatment equipment, must be designed in as space efficient manner as possible because horizontal square footage on an oil platform is scarce. Therefore, there is a need for water treatment equipment that can treat water at a fast rate, but which is also space efficient.
Organophilic clay has been used to absorb oil, as described in this assignees U.S. Pat. Nos. 6,398,951; 6,398,966; and 6,409,924. Further, published application US 2004/0112823 A1 describes a process for breaking aqueous hydrocarbon emulsions by contact with a polymeric foam material that absorbs oil and, after the polymer foam is saturated with oil, the polymer releases as much oil as it absorbs, but in larger, coalesced droplets.